JP7324225B2 - Method for producing masterbatch and rubber composition containing anion-modified cellulose nanofibers - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a masterbatch and a rubber composition containing a rubber component and anion-modified cellulose nanofibers.

Rubber compositions containing rubber and cellulosic fibers are known to have excellent mechanical strength. For example, Patent Document 1 describes a rubber/short fiber masterbatch obtained by stirring and mixing short cellulose fibers having an average fiber diameter of less than 0.5 μm and rubber latex. According to the document, a dispersion of short fibers having an average fiber diameter of less than 0.5 μm fibrillated in water is mixed with rubber latex and dried to produce a rubber/ It is said that a rubber composition having an excellent balance between rubber reinforcement and fatigue resistance can be produced from a short fiber masterbatch.

JP 2006-206864 A

As a method for fibrillating cellulose to reduce the average fiber diameter to nano-order (less than 1.0 μm), a method using a high-pressure homogenizer is generally known. High-pressure homogenizers are excellent in that they can easily apply high energy to the object to be treated, but they usually require extremely high pressure to reduce cellulose to nano-order average fiber diameters, and power consumption is reduced. becomes higher. If there is a method that can defibrate cellulose to a nano-order average fiber diameter with low power consumption in place of a high-pressure homogenizer, it will be possible to produce a rubber composition containing fibrillated cellulose with a small average fiber diameter at a lower cost. It is desirable because it enables manufacturing.

Further, when mixing short cellulose fibers with rubber, if the short fibers are heterogeneous, specifically, if large fibers that have not been completely defibrated remain, force is applied to the resulting rubber composition. In this case, the rubber tends to break starting from the portion where the large fibers remain. Therefore, it is preferred that the cellulosic fibers that are mixed with the rubber are homogeneous.

As a result of intensive studies by the present inventors, cellulose is anion-modified to obtain anion-modified cellulose, and this is defibrated using a cavitation jet device. It was found that anion-modified cellulose (anion-modified cellulose nanofibers) having an average fiber diameter of the order of magnitude can be obtained. Further, the present inventors have found that the strength of the rubber composition can be increased by including the anion-modified cellulose nanofibers in the rubber composition. The invention includes, but is not limited to:
(1) Step 1 of preparing anion-modified cellulose,
Step 2 of defibrating anion-modified cellulose to produce anion-modified cellulose nanofibers using a cavitation jet device, and Step 3 of mixing the anion-modified cellulose nanofibers obtained in step 2 with a rubber component to obtain a masterbatch. ,
A method of manufacturing a masterbatch, comprising:
(2) The cavitation jet device imparts an impact force to the anion-modified cellulose when the cavitation bubbles generated by the liquid jet jetted through the nozzle or orifice collapse, and the upstream pressure of the liquid jet jetted through the nozzle or orifice is The method according to (1), wherein the pressure is 0.01 MPa or more and 30.00 MPa or less, and the downstream pressure/upstream pressure ratio is 0.001 to 0.500.
(3) The method according to (1) or (2), wherein the anion-modified cellulose is cellulose having a carboxyl group.
(4) The method according to (3), wherein the amount of carboxyl groups in the anion-modified cellulose is 0.4 mmol/g to 3.0 mmol/g relative to the absolute dry mass of the anion-modified cellulose.
(5) The method according to (1) or (2), wherein the anion-modified cellulose is cellulose having a carboxymethyl group.
(6) The method according to (5), wherein the degree of carboxymethyl substitution in the anion-modified cellulose is 0.01 or more and less than 0.40.
(7) The method according to any one of (1) to (6), wherein the rubber component comprises a diene-based rubber polymer.
(8) A method for producing a rubber composition, comprising a step of producing a masterbatch by the method according to any one of (1) to (7), and a step of cross-linking the masterbatch.

Cellulose used for fibrillation is anion-modified cellulose, and this is fibrillated using a cavitation jet device, thereby producing anions having a nano-order average fiber diameter with less power consumption than when using a high-pressure homogenizer. A modified cellulose nanofiber can be obtained. In addition, the strength of the rubber composition can be increased by including the anion-modified cellulose nanofibers in the rubber composition.

In addition, when cellulose fibers are blended into a rubber composition, if the rubber composition is heterogeneous, such as a large amount of unfibrillated fibers remaining, in the final rubber composition, large unfibrillated fibers may be the starting points for breakage. However, since anion-modified cellulose nanofibers obtained by defibrating anion-modified cellulose using a cavitation jet apparatus are homogeneous, the above-mentioned problem is less likely to occur.

TECHNICAL FIELD The present invention relates to a method for producing a masterbatch and a rubber composition containing anion-modified cellulose nanofibers and a rubber component.

(1) Process 1
In step 1, anion-modified cellulose is provided. Anion-modified cellulose is obtained by introducing an anionic group into the molecular chain of cellulose. Specifically, an anionic group is introduced into the pyranose ring of cellulose by oxidation or substitution reaction.

(1-1) Cellulose The type of cellulose used as a raw material for anion-modified cellulose is not particularly limited. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding non-crystalline regions, etc., according to its origin, production method, and the like. Any of these celluloses can be used as a raw material in the present invention.

Examples of natural cellulose include bleached or unbleached pulp (bleached wood pulp or unbleached wood pulp); linters, purified linters; cellulose produced by microorganisms such as acetic acid bacteria. Raw materials for bleached or unbleached pulp are not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, and kenaf. Also, the method for producing the bleached pulp or the unbleached pulp is not particularly limited, and may be a mechanical method, a chemical method, or a combination of the two. Examples of bleached pulp or unbleached pulp classified by manufacturing method include mechanical pulp (thermomechanical pulp (TMP), groundwood pulp), chemical pulp (softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) ), softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP) and other kraft pulps). Further, dissolving pulp may be used in addition to paper pulp. Dissolving pulp is pulp that has been chemically refined, and is mainly used by dissolving it in chemicals, and serves as a main raw material for artificial fibers, cellophane, and the like.

Examples of regenerated cellulose include those obtained by dissolving cellulose in some solvent such as cuprammonium solution, cellulose xanthate solution, and morpholine derivative, and spinning again.

The fine cellulose is obtained by subjecting cellulosic materials such as the natural cellulose and regenerated cellulose to depolymerization (for example, acid hydrolysis, alkaline hydrolysis, enzymatic decomposition, explosion treatment, vibration ball mill treatment, etc.). and those obtained by mechanically processing the above cellulosic materials.

(1-2) Anion Modification Anion modification refers to the introduction of an anionic group into cellulose, specifically the introduction of an anionic group into the pyranose ring of cellulose by oxidation or substitution reaction. In the present invention, the oxidation reaction means a reaction of directly oxidizing a hydroxyl group of a pyranose ring to a carboxyl group. Further, in the present invention, a substitution reaction means a reaction for introducing an anionic group into a pyranose ring by a substitution reaction other than the oxidation.

(1-2-1) carboxylation (oxidation)
An example of anionic modification is carboxylation (introduction of carboxyl groups to cellulose, also referred to as "oxidation"). As used herein, a carboxyl group refers to -COOH (acid form) and -COOM (metal salt form) (wherein M is a metal ion). Carboxylated cellulose (also referred to as “oxidized cellulose”) can be obtained by carboxylating (oxidizing) the above cellulose raw material by a known method. Although not particularly limited, the amount of carboxyl groups is preferably 0.4 mmol/g to 3.0 mmol/g, more preferably 0.6 mmol/g to 2.0 mmol, relative to the absolute dry mass of anion-modified cellulose or anion-modified cellulose nanofibers. /g, more preferably 1.0 mmol/g to 2.0 mmol/g, and even more preferably 1.1 mmol/g to 2.0 mmol/g.

The carboxyl group content of anion-modified cellulose or anion-modified cellulose nanofibers can be measured by the following method:
60 ml of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose was prepared, and 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. and calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid, where the change in conductivity is gradual, using the following formula:
Carboxyl group amount [mmol/g carboxylated cellulose]=a [ml]×0.05/carboxylated cellulose mass [g].

As an example of a carboxylation (oxidation) method, a cellulose feedstock is oxidized in water with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides, and mixtures thereof. You can mention how to do it. This oxidation reaction selectively oxidizes the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface, resulting in a cellulose fiber having an aldehyde group and a carboxyl group (-COOH) or carboxylate group ( ^-COO- ) on the surface. can be obtained. Although the concentration of cellulose during the reaction is not particularly limited, it is preferably 5% by mass or less.

An N-oxyl compound means a compound capable of generating a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes the desired oxidation reaction. Examples include 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivatives (eg 4-hydroxy TEMPO). The amount of the N-oxyl compound to be used is not particularly limited as long as it is a catalytic amount that can oxidize the raw material cellulose. For example, it is preferably 0.01 mmol to 10 mmol, more preferably 0.01 mmol to 1 mmol, even more preferably 0.05 mmol to 0.5 mmol, relative to 1 g of absolute dry cellulose. Further, it is preferable that the concentration is about 0.1 mmol/L to 4 mmol/L with respect to the reaction system.

Bromides are compounds containing bromine, examples of which include alkali metal bromides that can be dissociated and ionized in water. Also, iodides are compounds containing iodine, examples of which include alkali metal iodides. The amount of bromide or iodide to be used can be selected within a range capable of promoting the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 mmol to 100 mmol, more preferably 0.1 mmol to 10 mmol, and even more preferably 0.5 mmol to 5 mmol, relative to 1 g of absolute dry cellulose. The modification is modification by an oxidation reaction.

Known oxidizing agents can be used, for example, halogens, hypohalous acids, halogenous acids, perhalogenates or salts thereof, halogen oxides, peroxides and the like can be used. Among them, sodium hypochlorite is preferable because it is inexpensive and has less environmental load. An appropriate amount of the oxidizing agent to be used is, for example, preferably 0.5 mmol to 500 mmol, more preferably 0.5 mmol to 50 mmol, even more preferably 1 mmol to 25 mmol, and most preferably 3 mmol to 10 mmol, relative to 1 g of absolute dry cellulose. . Further, for example, 1 mol to 40 mol is preferable with respect to 1 mol of the N-oxyl compound.

The oxidation process of cellulose allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4°C to 40°C, and may be room temperature of about 15°C to 30°C. Since carboxyl groups are generated in the cellulose as the reaction progresses, the pH of the reaction solution decreases. In order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8-12, preferably about 10-11. Water is preferable as the reaction medium because it is easy to handle and less likely to cause side reactions. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually 0.5 hours to 6 hours, for example, about 0.5 hours to 4 hours.

Moreover, the oxidation reaction may be carried out in two stages. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the reaction in the first step, again under the same or different reaction conditions, the reaction can be efficiently It can be oxidized well.

Another example of the carboxylation (oxidation) method is a method of oxidizing by contacting a cellulose raw material with an ozone-containing gas. This oxidation reaction oxidizes at least the hydroxyl groups at the 2- and 6-positions of the glucopyranose ring and causes degradation of the cellulose chain. The ozone concentration in the gas containing ozone is preferably 50 g/m ³ to 250 g/m ³ , more preferably 50 g/m ³ to 220 g/m ³ . The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. . The ozone treatment temperature is preferably 0°C to 50°C, more preferably 20°C to 50°C. The ozone treatment time is not particularly limited, but is about 1 minute to 360 minutes, preferably about 30 minutes to 360 minutes. When the ozone treatment conditions are within these ranges, cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. After the ozone treatment, additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the additional oxidation treatment is not particularly limited, but examples include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, these oxidizing agents can be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the cellulose raw material can be immersed in the solution for additional oxidation treatment.

The amount of carboxyl groups in the oxidized cellulose can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent added and the reaction time. The amount of carboxyl groups in the oxidized cellulose and the amount of carboxyl groups when the oxidized cellulose is used as nanofibers are usually the same.

(1-2-2) Carboxyalkylation An example of anion modification is the introduction of a carboxyalkyl group such as a carboxymethyl group. As used herein, a carboxyalkyl group refers to -RCOOH (acid form) and -RCOOM (metal salt form). Here, R is an alkylene group such as a methylene group or ethylene group, and M is a metal ion.

Carboxyalkylated cellulose may be obtained by a known method, or a commercially available product may be used. Preferably, the degree of carboxyalkyl substitution per anhydroglucose unit of the cellulose is less than 0.40. Furthermore, when the anionic group is a carboxymethyl group, the degree of carboxymethyl substitution is preferably less than 0.40. When the degree of substitution is 0.40 or more, the crystallinity of cellulose is lowered. Also, the lower limit of the degree of carboxyalkyl substitution is preferably 0.01 or more. Considering the workability, the degree of substitution is particularly preferably 0.02 or more and 0.35 or less, more preferably 0.10 or more and 0.35 or less, and 0.15 or more and 0.35 or less. is more preferable, and more preferably 0.15 or more and 0.30 or less. The anhydroglucose unit means an individual anhydroglucose (glucose residue) constituting cellulose, and the degree of carboxyalkyl substitution refers to the hydroxyl group (—OH) in the glucose residue constituting cellulose. The percentage of those substituted with ether groups (-ORCOOH or -ORCOOM) (the number of carboxyalkyl ether groups per glucose residue) is shown.

An example of a method for producing carboxyalkylated cellulose includes the following steps. The modification is modification by a substitution reaction. Carboxymethylated cellulose will be described as an example.
i) Mixing the raw material with the solvent and the mercerizing agent, and mercerizing at a reaction temperature of 0° C. to 70° C., preferably 10° C. to 60° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. the process of processing,
ii) then, 0.05 to 10.0 times mol of a carboxymethylating agent per glucose residue is added, the reaction temperature is 30° C. to 90° C., preferably 40° C. to 80° C., and the reaction time is 30 minutes to 10 hours; A step of conducting the etherification reaction preferably for 1 hour to 4 hours.

The above-mentioned cellulose raw material can be used as the bottom raw material. As the solvent, 3 to 20 times by weight of water or a lower alcohol, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc. alone, or two Mixed media of more than one species can be used. When a lower alcohol is mixed, the mixing ratio is preferably 60% by mass to 95% by mass. As the mercerizing agent, it is preferable to use an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, in an amount of 0.5 to 20 times the moles of the anhydroglucose residue of the starting material.

As described above, the degree of carboxymethyl substitution per glucose unit of cellulose is less than 0.40, preferably 0.01 or more and less than 0.40. By introducing carboxymethyl substituents into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which carboxymethyl substituents have been introduced can be nano-fibrillated. If the number of carboxymethyl substituents per glucose unit is less than 0.01, nano-fibrillation may not be sufficient. The degree of carboxymethyl substitution is more preferably 0.10 or more and less than 0.40, still more preferably 0.15 or more and less than 0.40, still more preferably 0.20 or more and less than 0.40. The degree of carboxyalkyl substitution in the carboxyalkylated cellulose is generally the same as the degree of carboxyalkyl substitution when the carboxyalkylated cellulose is made into nanofibers.

The degree of carboxymethyl substitution per glucose unit can be measured by the following method:
About 2.0 g of carboxymethylated cellulose (absolute dry) is precisely weighed and placed in a 300 mL conical flask with a common stopper. 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 900 mL of methanol is added and shaken for 3 hours to convert carboxymethylated cellulose salt (CM cellulose) into hydrogenated CM cellulose. 1.5 g to 2.0 g of hydrogenated CM cellulose (absolutely dried) is accurately weighed and placed in a 300 mL Erlenmeyer flask equipped with a common stopper. Hydrogenated CM-cellulose is wetted with 15 mL of 80% by mass methanol, 100 mL of 0.1 N NaOH is added, and shaken at room temperature for 3 hours. Excess NaOH was back-titrated with 0.1N _H2SO4 using phenolphthalein as _an indicator. The degree of carboxymethyl substitution (DS) is calculated by the formula:
A=[(100×F′−(0.1N H ₂ SO ₄ ) (mL)×F)×0.1]/(absolute dry mass of hydrogen-type CM cellulose (g))
DS = 0.162 x A/(1 - 0.058 x A)
A: Amount of 1N NaOH (mL) required to neutralize 1 g of hydrogenated CM-cellulose
F: factor of 0.1N _H2SO4 F': factor of 0.1N _NaOH .

The degree of substitution with carboxyalkyl groups other than carboxymethyl groups can also be measured in the same manner as described above.

(1-2-3) Esterification One example of anion modification is esterification. Examples of the esterification method include a method of mixing a cellulose raw material with powder or an aqueous solution of a phosphoric acid compound, a method of adding an aqueous solution of a phosphoric acid compound to a slurry of a cellulose raw material, and the like. Phosphoric acid compounds include phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among the above, a compound having a phosphate group is preferable because it is low cost, easy to handle, and can introduce a phosphate group into the cellulose of the pulp fiber to improve defibration efficiency. Compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite , sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate , ammonium pyrophosphate, ammonium metaphosphate and the like. Phosphate groups can be introduced into cellulose by using one or more of these in combination. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid, from the viewpoint of high efficiency of introduction of phosphate groups, easy fibrillation in the fibrillation process described below, and easy industrial application is preferred. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Further, it is desirable to use the phosphoric acid-based compound in the form of an aqueous solution, since the reaction can proceed uniformly and the efficiency of introduction of the phosphoric acid group is increased. The pH of the aqueous solution of the phosphoric acid-based compound is preferably 7 or less because the efficiency of introducing phosphoric acid groups is increased, but from the viewpoint of suppressing hydrolysis of pulp fibers, pH 3 to 7 is preferable.

Examples of the method for producing the phosphorylated cellulose include the following method. A phosphoric acid-based compound is added to a suspension of a cellulose raw material having a solid concentration of 0.1% by mass to 10% by mass while stirring to introduce a phosphoric acid group into the cellulose. When the cellulose raw material is 100 parts by mass, the amount of the phosphoric acid compound added is preferably 0.2 parts by mass to 500 parts by mass, and is preferably 1 part by mass to 400 parts by mass. more preferred. If the proportion of the phosphoric acid-based compound is at least the lower limit, the yield of fine fibrous cellulose can be further improved. However, if the above upper limit is exceeded, the effect of improving the yield reaches a ceiling, which is not preferable from the viewpoint of cost.

In addition to the phosphoric acid-based compound, powders or aqueous solutions of other compounds may be mixed. The compound other than the phosphoric acid-based compound is not particularly limited, but a basic nitrogen-containing compound is preferable. "Basic" here is defined as a pink to red color of the aqueous solution in the presence of the phenolphthalein indicator or pH of the aqueous solution greater than 7. The basic nitrogen-containing compound used in the present invention is not particularly limited as long as the effect of the present invention is exhibited, but a compound having an amino group is preferable. Examples include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like. Among them, urea is preferable because it is inexpensive and easy to handle. The amount of the other compound added is preferably 2 parts by mass to 1000 parts by mass, more preferably 100 parts by mass to 700 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0°C to 95°C, more preferably 30°C to 90°C. Although the reaction time is not particularly limited, it is about 1 minute to 600 minutes, more preferably 30 minutes to 480 minutes. When the esterification reaction conditions are within these ranges, cellulose can be prevented from being excessively esterified and easily dissolved, and the yield of phosphate-esterified cellulose is improved. After dehydrating the obtained phosphate-esterified cellulose suspension, it is preferable to heat-treat at 100° C. to 170° C. from the viewpoint of suppressing hydrolysis of cellulose. Further, it is preferable to heat at 130° C. or less, preferably 110° C. or less while water is contained in the heat treatment, and heat at 100° C. to 170° C. after removing the water.

The degree of phosphate group substitution per glucose unit of the phosphated cellulose is preferably 0.001 or more and less than 0.40. By introducing a phosphate group substituent into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which a phosphate group has been introduced can be easily nano-fibrillated. If the degree of phosphate group substitution per glucose unit is less than 0.001, sufficient nanofibrillation cannot be achieved. On the other hand, if the degree of phosphate group substitution per glucose unit is greater than 0.40, the nanofibers may not be obtained due to swelling or dissolution. In order to efficiently defibrate, it is preferable to wash the phosphated cellulose raw material obtained above with cold water after boiling. Modification by these esterifications is modification by a substitution reaction. The degree of substitution in the esterified cellulose and the degree of substitution when the same esterified cellulose is made into nanofibers are usually the same.

The degree of phosphate group substitution per glucose unit can be measured by the following method:
A slurry of phosphorylated cellulose having a solids content of 0.2% by weight is prepared. Next, to the slurry, 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo, conditioned) was added, shaken for 1 hour, and then poured onto a mesh with an opening of 90 μm. The phosphate-esterified cellulose is converted to a hydrogen-type phosphate-esterified cellulose by separating the resin and the slurry at . Next, while adding 50 μL of 0.1 N sodium hydroxide aqueous solution to the slurry after the treatment with the ion-exchange resin once every 30 seconds, the change in the electrical conductivity of the slurry is measured. Among the measurement results, by dividing the amount of alkali (mmol) required in the region where the electrical conductivity suddenly decreases by the solid content (g) in the slurry to be titrated, the hydrogen-type phosphate-esterified cellulose per 1 g Calculate the amount of phosphate groups (mmol/g). Furthermore, the degree of phosphate group substitution (DS) per glucose unit of the phosphorylated cellulose is calculated by the following formula:
DS = 0.162 x A/(1 - 0.079 x A)
A: Phosphate group content per gram of hydrogen-type phosphate-esterified cellulose (mmol/g).

(1-3) Anion-Modified Cellulose Anion-modified cellulose can be obtained by anion-modifying the raw material cellulose as exemplified above. Moreover, you may use a commercial thing. As the type of anion-modified cellulose, cellulose having a carboxyl group or cellulose having a carboxyalkyl group is preferable. In particular, carboxylated cellulose obtained by oxidizing cellulose using an N-oxyl compound and an oxidizing agent has carboxyl groups uniformly introduced, is easily disentangled uniformly, and has high transparency. is preferable in terms of obtaining

As the anion-modified cellulose, one that maintains at least a part of its fibrous shape even when dispersed in water or a water-soluble organic solvent is used. Nanofibers cannot be obtained by using materials that do not maintain their fibrous shape (that is, materials that dissolve). The expression that at least a part of the fibrous shape is maintained when dispersed means that a fibrous substance can be observed when an anion-modified cellulose dispersion is observed with an electron microscope. In addition, anion-modified cellulose is preferable, since a peak of cellulose type I crystals can be observed when measured by X-ray diffraction.

The degree of crystallinity of cellulose in the anion-modified cellulose is preferably 50% or more, more preferably 60% or more for crystalline type I. By adjusting the crystallinity to the above range, it is possible to sufficiently obtain crystalline cellulose fibers that do not dissolve even after the fibers are refined by fibrillation. The crystallinity of cellulose can be controlled by the crystallinity of the raw material cellulose and the degree of anion modification. The method for measuring the crystallinity of anion-modified cellulose is as follows:
A sample is placed in a glass cell and measured using an X-ray diffraction measurement device (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity is calculated using the method of Segal et al. Using the diffraction intensity at 2θ = 10° to 30° in the X-ray diffraction diagram as a baseline, the diffraction intensity of the 002 plane at 2θ = 22.6° and 2θ = It is calculated from the diffraction intensity of the amorphous portion at 18.5° by the following equation.
Xc=(I002c−Ia)/I002c×100
Xc: Crystallinity of type I of cellulose (%)
I002c: 2θ=22.6°, diffraction intensity of 002 plane Ia: 2θ=18.5°, diffraction intensity of amorphous portion.

The proportion of cellulose type I crystals in the anion-modified cellulose and the proportion of cellulose type I crystals when the anion-modified cellulose is used as nanofibers are usually the same.

(2) Process 2
In step 2, anion-modified cellulose nanofibers are produced by treating (fibrillating) the anion-modified cellulose using a cavitation jet device.

(2-1) Anion-Modified Cellulose Dispersion For fibrillation, an anion-modified cellulose dispersion is prepared. Water, an organic solvent, or a mixture thereof can be appropriately selected as the dispersion medium. Although the type of organic solvent is not limited, polar solvents having a high affinity for hydroxyl groups in cellulose are preferred, such as methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl cellosolve, ethyl cellosolve, ethylene glycol. , glycerin, ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and the like. The dispersion medium may be used alone, or two or more of them may be mixed and used. For example, a form in which two or more kinds of organic solvents are mixed, a form in which water and an organic solvent are contained, a form in which only water is used, or the like can be appropriately selected. Using only water as the dispersion medium (ie, 100% water) is preferred for ease of handling. When water and an organic solvent are mixed, the mixing ratio is not particularly limited, and the mixing ratio may be appropriately adjusted according to the type of organic solvent used.

The solid content concentration of the anion-modified cellulose dispersion to be subjected to the cavitation jet apparatus is preferably 10.0% by mass or less, more preferably 7.0% by mass or less, and still more preferably 0.1 to 5.0% by mass. From the point of view of bubble generation efficiency, treatment within the range is preferred.

The pH of the anion-modified cellulose dispersion is preferably pH 6-13, more preferably pH 6-12, and even more preferably pH 6-10. If the pH is 6 or more, defibration of the anion-modified cellulose is likely to proceed. On the other hand, if the pH exceeds 13, alkaline scorching of the pulp fibers will occur and the whiteness will decrease, which is not preferable.

(2-2) Cavitation jet device A cavitation jet device compresses the jet liquid and jets it from the tip of the nozzle at high speed toward the liquid to be jetted. This device shreds solid masses in the liquid to be jetted and the liquid to be jetted by the collapsing energy of cavitation bubbles generated by the expansion of the liquid. Since there is no physical contact with the fibers such as blades, the fibers are less likely to be shortened.

As the injection liquid, the dispersion medium used for the anion-modified cellulose dispersion or the anion-modified cellulose dispersion itself can be used. As the liquid to be jetted, the anion-modified cellulose dispersion described above is used. The jetted liquid is jetted toward the anion-modified cellulose dispersion, which is the liquid to be jetted, to generate a jet flow, thereby generating cavitation in the liquid to be jetted, and the anion-modified cellulose in the liquid to be jetted by the collapse energy of the cavitation bubbles. can be defibrated. It is preferable to use an anion-modified cellulose dispersion as the injection liquid from the viewpoint of efficient defibration. When an anion-modified cellulose dispersion is used as the injection liquid, in addition to the effects of cavitation generated around the jet, hydrodynamic shear force can be obtained when the liquid is injected from a nozzle or orifice at high pressure, resulting in efficient defibration. be able to.

Cavitation occurs when a liquid is accelerated such that the local pressure is lower than the liquid's vapor pressure, so flow velocity and pressure are important to control the occurrence of cavitation. A basic non-dimensional number representing a cavitation state, the cavitation number σ, is defined as the following Equation 1 (edited by Yoji Kato, Cavitation Basics and Recent Advances, New Edition, Maki Shoten, 1999).

A large cavitation number indicates that the flow field is in a state where cavitation is unlikely to occur. When cavitation is generated through a nozzle or orifice such as a cavitation jet, the cavitation number σ is calculated from the upstream pressure p ₁ of the nozzle or orifice, the downstream pressure p ₂ of the nozzle or orifice, _and the saturated vapor pressure pv of the sample water. It can be rewritten as Equation 2 below, and in a cavitation jet, the pressure difference between p ₁ , p ₂ , and p _v is large, and p ₁ >> p ₂ >> p _v , so the cavitation number σ can be further approximated to p ₂ /p ₁ (H. Soyama, J. Soc. Mat. Sci. Japan, 47(4), 381 1998).

In the present invention, the cavitation condition is that the cavitation number σ (that is, downstream pressure/upstream pressure) that can be approximated to p ₂ /p ₁ described above is preferably 0.001 or more and 0.500 or less, It is preferably 0.003 or more and 0.200 or less, and particularly preferably 0.010 or more and 0.100 or less. When the cavitation number σ is less than 0.001, the pressure difference with the surroundings when the cavitation bubbles collapse is low, so the defibration effect is small. Cavitation is less likely to occur.

When cavitation is generated by injecting the injection liquid through the nozzle or orifice, the pressure of the injection liquid (upstream pressure) is preferably 0.01 MPa or more and 30.00 MPa or less, and more preferably 0.70 MPa or more and 20.00 MPa or less. is preferably 2.00 MPa or more and 10.00 MPa or less is particularly preferable. If the upstream pressure is less than 0.01 MPa, it is difficult to generate a pressure difference with the downstream pressure, and the effect is small. Moreover, when the pressure is higher than 30.00 MPa, the energy consumption increases, which is disadvantageous in terms of cost. On the other hand, the pressure in the container (downstream pressure) is preferably 0.05 MPa or more and 0.50 MPa or less in terms of static pressure.

The jetting speed of the ejected liquid is desirably in the range of 1 m/sec to 200 m/sec, and preferably in the range of 20 m/sec to 100 m/sec. If the jet velocity is less than 1 m/sec, the effect is weak because the pressure drop is low and cavitation is less likely to occur. On the other hand, if it is more than 200 m/sec, a high pressure is required and a special device is required, which is disadvantageous in terms of cost.

A cavitation jet device has a pipe or container of a certain width, which is a place where cavitation occurs, immediately after a nozzle or orifice for injecting liquid. If the inner diameter of the pipe immediately after this nozzle or orifice (the inner diameter without the wall thickness of the pipe or container) is comparable to the maximum width of the cavitation jet produced by the liquid jet ejected through the nozzle or orifice, the anion modification This is preferable because defibration of cellulose proceeds efficiently. For example, the maximum width of a cavitation jet generated by a liquid jet jetted through a nozzle or orifice is preferably adjusted to a length of 50% or more of the inner diameter of the pipe immediately after the nozzle or orifice, more preferably 55% or more, 60% or more is more preferable, 65% or more is still more preferable, 70% or more is still more preferable, 80% or more is still more preferable, and 85% or more is even more preferable. Also, the length is preferably adjusted to 130% or less, more preferably 110% or less, and more preferably less than 100%. Here, a nozzle is a pipe-shaped component for injecting a liquid in a certain direction. It refers to the part that is ejected by An orifice is a hole cut in a wall for ejecting a liquid. When a liquid is injected from a nozzle or orifice, a group of cavitation bubbles generated by the liquid jet appears in a cone shape with the exit of the nozzle or orifice as the apex. This group of cavitation bubbles is called a cavitation jet. The maximum width of the cavitating jet refers to the maximum width (diameter) of the cavitating jet perpendicular to the injection direction. The maximum width of the cavitation jet varies depending on conditions such as the nozzle or orifice used, the liquid to be injected, the liquid to be injected, the injection speed, the downstream/upstream pressure ratio, and the temperature. When measuring the maximum width of the cavitation jet, if the width of the cavitation jet is large and it contacts the inner wall of the pipe immediately after the nozzle or orifice, use a larger pipe so that the cavitation jet does not contact the inner wall under the same conditions. Injection is performed and the maximum width of the cavitation jet is determined. Further, a plurality of nozzles or orifices may be connected to the piping immediately after the nozzles or orifices, and liquid may be injected into the piping from each nozzle or orifice to generate a plurality of cavitation jets. The maximum width of the cavitation jet refers to the maximum width when the cavitation jet generated from each nozzle or orifice is regarded as one cavitation jet. That is, when a plurality of cavitating jets are merged at their ends, the maximum width of the merged cavitating jets, and when at least some of the plurality of cavitating jets are independent of each other without being merged, is the maximum width obtained by connecting the positions of the outermost cavitation jets observed (the side away from the center of the plane perpendicular to the jetting direction of each jet toward the inner wall side of the pipe). .

Also, the piping immediately after the nozzle or orifice refers to any vessel or piping to which the nozzle or orifice is connected and where the cavitation jet is formed. The shape of the pipe may be cylindrical, prismatic, conical, pyramidal, or the like, but a cylindrical shape is preferred in order to prevent the fibers from stagnation after fibrillation. The pipe diameter immediately after the nozzle or orifice refers to the width (inner diameter of the pipe) perpendicular to the injection direction of the cavitation jet in the pipe. When the pipe has a tubular shape other than a cylindrical shape, such as a rectangular tubular shape, the minimum width among the widths perpendicular to the jetting direction of the cavitation jet is used. In addition, when the pipe is conical or pyramidal, it means the pipe diameter of the cross section that maximizes the width of the cavitation jet (when the pipe is pyramidal, the minimum width of the same cross section).

If the maximum width of the cavitation jet generated by the liquid jet injected through the nozzle or orifice is less than 50% of the inner diameter of the pipe immediately after the nozzle or orifice, the pipe (or container) immediately after the nozzle or orifice is not affected by the cavitation jet. On the other hand, since it is too large, the anion-modified cellulose and the anion-modified cellulose nanofibers remain in the pipe (or container), making defibration difficult. On the other hand, if the length exceeds 130%, a large portion of the cavitation jet may directly contact the piping directly behind the nozzle or orifice, causing erosion of the piping. When the maximum width of the cavitation jet is 100% or more and 130% or less of the inner diameter of the pipe immediately after the nozzle or orifice, part of the cavitation jet (end) comes into contact with the pipe immediately after the nozzle or orifice. , the contact is partial, and the impact of the end of the cavitation jet (the part far from the nozzle or orifice) is rather weak, so it can be used because it has little effect on the piping. If the maximum width of the cavitation jet is less than 100% of the inner diameter of the pipe directly behind the nozzle or orifice, it is preferable because the pipe immediately after the nozzle or orifice will not be eroded.

The ratio between the maximum width of the cavitation jet and the inner diameter of the pipe immediately after the nozzle or orifice can be adjusted by adjusting the inner diameter of the pipe immediately after the nozzle or orifice, adjusting the above-mentioned downstream pressure/upstream pressure ratio, or It can be adjusted by changing the maximum width of the cavitation jet such as by adjusting the ejection speed of the ejected liquid.

The injection of the liquid to generate cavitation may be done in a container open to the atmosphere such as a pulper, but is preferably done in a pressure vessel to control cavitation.

Cavitation is affected by the amount of gas in the liquid, and if there is too much gas, bubbles collide and coalesce, creating a cushion effect in which the collapsing impact force is absorbed by other bubbles, thereby weakening the impact force. Since the amount of gas in the liquid is affected by dissolved gas and vapor pressure, it is preferable to adjust the impact force of cavitation by controlling the treatment temperature within a certain range. The treatment temperature is preferably 0° C. or higher and 70° C. or lower, more preferably 10° C. or higher and 60° C. or lower, although it depends on the type of dispersion medium. In general, the impact force is considered to be maximum at the midpoint between the melting point and the boiling point. Therefore, when water is used as the dispersion medium, a temperature of around 50 ° C. is suitable, but even if the temperature is other than that, it is within the above range. A sufficient defibration effect can be obtained.

A surfactant may be added to the jetting liquid and/or the jetted liquid to reduce the energy required to generate cavitation. The surfactant to be used is not particularly limited. surfactants, cationic surfactants, amphoteric surfactants, and the like. These may be used singly or in combination of two or more. When a surfactant is added, the amount to be added may be an amount necessary to reduce the surface tension of the liquid to be jetted and/or the liquid to be jetted.

The treatment with the cavitation jet device may be repeated multiple times until the desired degree of fibrillation is achieved. When the treatment is carried out a plurality of times, it may be circulated in one apparatus for the required number of times, a plurality of apparatuses may be used in parallel, or the treatment may be performed by sequentially flowing through a plurality of apparatuses.

(2-3) Anion-Modified Cellulose Nanofibers Nanofibers can be obtained by defibrating anion-modified cellulose to a nano-order average fiber diameter by fibrillation using the above-described cavitation jet apparatus. The nano-order average fiber diameter refers to an average fiber diameter of less than 1 μm. In the present invention, the anion-modified cellulose nanofiber preferably has an average fiber diameter of about 3 nm to 500 nm, more preferably about 3 nm to 150 nm, still more preferably about 3 nm to 20 nm. The aspect ratio is 30 or more, preferably 50 or more, more preferably 100 or more. Although the upper limit of the aspect ratio is not limited, it is about 500 or less.

The average fiber diameter and average fiber length of the anion-modified cellulose nanofibers are measured using an atomic force microscope (AFM) when the diameter is less than 20 nm, and a field emission scanning electron microscope (FE-SEM) when the diameter is 20 nm or more. It can be measured by analyzing 200 randomly selected fibers and calculating the average. Also, the aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length/average fiber diameter.

As the anion-modified cellulose nanofibers, those having high transparency when made into a dispersion are preferable. Transparency is measured, for example, in the following way:
A cellulose nanofiber dispersion with a predetermined concentration is prepared, and a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) is used to measure the transmittance (% ) is measured and taken as transparency.

In the present invention, for example, for an anion-modified cellulose nanofiber dispersion having a solid content of 1.0% by mass with water as a dispersion medium, the content is preferably 70% or more, more preferably 80% or more, and 90%. It is more preferable that it is above. A high degree of transparency means that the amount of unfibrillated fibers is small and the fibrillation proceeds uniformly. If unfibrillated large fibers remain, when mixed with a rubber component to obtain a rubber composition, a problem may occur in that the rubber tends to break starting from the large fibers in the rubber composition. Anion-modified cellulose nanofibers, which have high transparency and are uniformly defibrated, are preferable because such problems are less likely to occur. Although the upper limit of transparency is not particularly limited, it is, for example, 99%.

Although the viscosity of the anion-modified cellulose nanofiber is not particularly limited, it is preferable that the viscosity becomes high when it is dispersed. Viscosity is measured, for example, by the following method:
A cellulose nanofiber dispersion with a predetermined concentration is prepared, and according to the method of JIS-Z-8803, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), at 25 ° C., rotation speed 60 rpm or 3 at 6 rpm. Measure the value after minutes.

For example, for an anion-modified cellulose nanofiber dispersion with a solid content of 1.0% by mass using water as a dispersion medium, the B-type viscosity at 6 rpm measured by the above method is 5000 mPa s or more, or 7000 mPa s or more, or It may be 10000 mPa s or more, 15000 mPa s or more, or 17000 mPa s or more, and the B-type viscosity at 60 rpm is 1000 mPa s or more, 2000 mPa s or more, or 3000 mPa s or more, or It may be 4000 mPa·s or more. However, it is not limited to these. A high viscosity means less fiber damage during fibrillation. Since the cavitation jet device has a lower processing pressure than the ultrahigh pressure homogenizer, it is thought that the fibers are less damaged during fibrillation. The upper limit of viscosity is not particularly limited.

(3) Process 3
In step 3, the anion-modified cellulose nanofibers obtained in step 2 are mixed with a rubber component to produce a masterbatch.

(3-1) Rubber component A rubber component is a raw material of rubber that is crosslinked to form rubber. Although there are rubber components for natural rubber and rubber components for synthetic rubber, either one may be used in the present invention, or both may be used in combination. For convenience, rubber components such as those for natural rubber are referred to as "natural rubber polymers" and the like.

Natural rubber (NR) polymers include narrowly defined natural rubber polymers that are not chemically modified; chemically modified natural rubber polymers such as chlorinated natural rubber polymers, chlorosulfonated natural rubber polymers, and epoxidized natural rubber polymers; hydrogenated natural rubber polymers; Rubber polymers; include deproteinized natural rubber polymers. Examples of synthetic rubber polymers include butadiene rubber (BR) polymers, styrene-butadiene copolymer rubber (SBR) polymers, isoprene rubber (IR) polymers, acrylonitrile-butadiene rubber (NBR) polymers, chloroprene rubber (CR) polymers, styrene - diene-based rubber polymers such as isoprene copolymer rubber polymers, styrene-isoprene-butadiene copolymer rubber polymers, isoprene-butadiene copolymer rubber polymers; butyl rubber (IIR) polymers, ethylene-propylene rubber (EPM, EPDM) polymers , acrylic rubber (ACM) polymer, epichlorohydrin rubber (CO, ECO) polymer, fluororubber (FKM) polymer, silicone rubber (Q) polymer, urethane rubber (U) polymer, chlorosulfonated polyethylene (CSM) polymer, etc. Examples include non-diene rubber polymers. One of these rubber polymers may be used alone, or two or more of them may be used in combination. Among these, diene-based rubber polymers including natural rubber (NR) polymers are particularly preferable from the viewpoint of reinforcing properties. Preferred diene-based rubber polymers include natural rubber (NR) polymers, isoprene rubber (IR) polymers, butadiene rubber (BR) polymers, styrene-butadiene copolymer rubber (SBR) polymers, butyl rubber (IIR) polymers, acrylonitrile-butadiene. Rubber (NBR) polymers, modified natural rubber polymers as described above, and the like.

The rubber component may be mixed as it is, or may be mixed in the form of a dispersion (latex) in which the rubber component is dispersed in a dispersion medium, or in the form of a solution in which the rubber component is dissolved in a solvent. Examples of the dispersion medium and solvent (hereinafter collectively referred to as "liquid medium") include water and organic solvents. The amount of the liquid medium is preferably 10 to 1000 parts by mass with respect to 100 parts by mass of the rubber component.

(3-2) Form of cellulose nanofibers to be mixed with rubber component The form of cellulose nanofibers to be mixed with the rubber component is not particularly limited. For example, a dispersion of anion-modified cellulose nanofibers, a dry solid of the dispersion, and a wet solid of the dispersion may be subjected to mixing. The concentration of cellulose nanofibers in the dispersion can be 0.1 to 5.0% by mass when the dispersion medium is water. When the dispersion medium contains an organic solvent such as alcohol in addition to water, the concentration may be 0.1 to 20.0% by mass. Wet solids are intermediate forms of solids between the dispersions and dry solids. The amount of the dispersion medium in the wet solids obtained by dehydrating the dispersion by a conventional method may be about 5 to 15% by mass with respect to the cellulose nanofibers. You may adjust the quantity of a dispersion medium suitably.

Also, the cellulose nanofibers mixed with the rubber component may be a mixture of a cellulose nanofiber dispersion and a water-soluble polymer, a dry solid of the mixture, or a wet solid of the mixture. The amount of liquid medium in the mixtures and dry solids may be in the ranges described above. Examples of water-soluble polymers include cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, pullulan, starch, potato starch, and kudzu. Flour, positive starch, phosphorylated starch, cornstarch, gum arabic, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soybean protein lysate, peptone, polyvinyl alcohol, polyacrylamide, polysodium acrylate , polyvinylpyrrolidone, polyvinyl acetate, polyamino acid, polylactic acid, polymalic acid, polyglycerin, latex, rosin-based sizing agent, petroleum resin-based sizing agent, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide/polyamine resin, Polyethylenimines, polyamines, vegetable gums, polyethylene oxides, hydrophilic crosslinked polymers, polyacrylates, starch polyacrylic acid copolymers, tamarind gum, guar gum, and colloidal silica, and mixtures thereof. Among these, carboxymethylcellulose or a salt thereof is preferable from the point of solubility. Carboxymethyl cellulose here is completely dissolved in water and does not have a fiber shape in water, and is distinguished from carboxymethylated cellulose nanofibers having a fiber shape in water.

The dry solids and wet solids can be prepared by drying a cellulose nanofiber dispersion or a mixture of a cellulose nanofiber dispersion and a water-soluble polymer. The drying method is not particularly limited, and examples thereof include spray drying, pressing, air drying, hot air drying, and vacuum drying. Examples of drying equipment include continuous tunnel drying equipment, band drying equipment, vertical drying equipment, vertical turbo drying equipment, multistage disk drying equipment, ventilation drying equipment, rotary drying equipment, flash drying equipment, and spray dryer drying equipment. , spray drying equipment, cylinder drying equipment, drum drying equipment, screw conveyor drying equipment, rotary drying equipment with heating tubes, vibration transport drying equipment, etc., batch type box drying equipment, ventilation drying equipment, vacuum box drying equipment, or A stirring drying device and the like can be mentioned. These drying devices may be used alone or in combination of two or more. A drum dryer is preferable because it can directly and uniformly supply heat energy to the material to be dried, so that it has high energy efficiency and can immediately recover the dried material without applying excessive heat.

The mixing ratio of the anion-modified cellulose nanofibers and the rubber component may be adjusted so as to achieve the ratio of the rubber composition described later. The fiber (solid content) is preferably 0.1 to 100.0 parts by mass.

(3-3) Other compounding agents In step 3, in addition to the rubber component and cellulose nanofibers, other compounding agents may be mixed. Examples of other compounding agents include, but are not limited to, reinforcing agents (carbon black, silica, etc.), silane coupling agents, cross-linking agents (sulfur, peroxides, etc.), vulcanization accelerators (zinc oxide, stearin acids, sulfenamides, etc.), vulcanization accelerator aids, oils, cured resins, waxes, antioxidants, peptizers, colorants, pH adjusters, and other compounding agents that can be used in the rubber industry. Sulfenamides of vulcanization accelerators include, for example, Nt-butyl-2-benzothiazolesulfenamide.

When sulfur is blended, the amount is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 1.7% by mass or more relative to the rubber component. The upper limit is preferably 10% by mass or less, preferably 7% by mass or less, and more preferably 5% by mass or less.

When blending a vulcanization accelerator, the blending amount is preferably 0.1% by mass, more preferably 0.3% by mass or more, and even more preferably 0.4% by mass or more, relative to the rubber component. The upper limit is preferably 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less.

(3-4) Mixing A masterbatch is produced by mixing the anion-modified cellulose nanofibers and the rubber component described above with the other compounding agents described above, if necessary.

The order of adding the ingredients in the mixing is not particularly limited, and each component may be mixed at once, or one of the ingredients may be mixed first, and then the remaining ingredients may be mixed. A first example is a method in which the anion-modified cellulose nanofibers and the rubber component are first mixed, and then the resulting masterbatch is mixed with other compounding agents. Specifically, for example, an anion-modified cellulose nanofiber dispersion and a rubber component dispersion (latex) are mixed (eg, stirred by a mixer or the like), water is removed, and the resulting mixture is added to other formulations. Add the agent and knead (eg, open roll device). Thereby, the anion-modified cellulose nanofibers can be uniformly dispersed in the rubber component.

A second example is a method of mixing anion-modified cellulose nanofibers, a rubber component, and other ingredients at once and removing water. Specifically, for example, an anion-modified cellulose nanofiber dispersion, a rubber component dispersion (latex), and other compounding agents are mixed (eg, stirred by a mixer or the like), and water is removed from the resulting mixture. Thereby, any component can be uniformly dispersed.

The method of removing water from the mixture is not particularly limited, and examples thereof include a method of drying in a dryer such as an oven, and a method of adjusting the pH to 2 to 6 to coagulate, then dehydrating and drying.

A third example is a method in which other components are added to the rubber component in any order and mixed. Specifically, for example, solids of anion-modified cellulose nanofibers and other compounding agents are mixed in an arbitrary order with solids of the rubber component, and the mixture is similarly kneaded with a device such as an open roll. Thereby, the step of removing water can be omitted.

Examples of masticating and kneading devices include Banbury mixers, kneaders, open rolls, and the like.

The temperature during mixing (for example, during mastication and kneading) may be about room temperature (about 15 to 30° C.), or may be heated at a high temperature to the extent that the rubber component does not undergo a cross-linking reaction. For example, it is 140° C. or lower, more preferably 120° C. or lower. The lower limit is 70°C or higher, preferably 80°C or higher. Therefore, the heating temperature is preferably about 80 to 140°C, more preferably about 80 to 120°C.

After completion of mixing, molding may be performed as necessary. Examples of the molding apparatus include mold molding, injection molding, extrusion molding, hollow molding, foam molding, and the like, and may be appropriately selected according to the final product shape, application, and molding method.

(3-5) Masterbatch A masterbatch can be produced by the method described above. A masterbatch is a rubber precursor and refers to a composition containing an uncrosslinked rubber component that can be crosslinked to form a rubber. In the present specification, the masterbatch contains at least an uncrosslinked rubber component and anion-modified cellulose nanofibers, and other compounding agents containing sulfur and vulcanization accelerators may be added, It may be in a state before being added. Moreover, it may be molded according to the form of the final product, or it may be in a state before being molded.

(4) Manufacture of rubber composition The masterbatch can be converted into a rubber composition by cross-linking the masterbatch to which a cross-linking agent has been added.

(4-1) Cross-linking Cross-linking may be carried out under conditions where the cross-linking reaction proceeds, and conditions such as temperature are not particularly limited. In general, the heating temperature is preferably 140° C. or higher, preferably 200° C. or lower, and more preferably 180° C. or lower. Therefore, the heating temperature is preferably about 140 to 200.degree. C., more preferably about 140 to 180.degree. For cross-linking, for example, but not limited to, a vulcanization apparatus that performs die vulcanization, can vulcanization, continuous vulcanization, and the like can be used. The rubber composition of the present invention tends to undergo a cross-linking reaction more rapidly than a composition containing no cellulose nanofibers. Although the reason for this is not limited, it is presumed that functional groups such as carboxyl groups in the cellulose nanofibers promote the cross-linking reaction.

After cross-linking, finishing treatment may be carried out, if necessary, before the final product is obtained. Finishing treatments include, for example, polishing, surface treatment, lip finishing, lip cutting, chlorine treatment, etc. Only one of these treatments may be performed, or two or more of them may be combined.

(4-2) Rubber Composition As used herein, the term "rubber composition" refers to a composition obtained by crosslinking the masterbatch described above. The content of the anion-modified cellulose nanofiber (solid content) in the rubber composition is preferably 0.1 to 100.0 parts by mass with respect to 100.0 parts by mass of the rubber component. From the viewpoint of improving tensile strength, the content is more preferably 1.0 parts by mass or more, still more preferably 2.0 parts by mass or more, and 3.0 parts by mass or more with respect to 100.0 parts by mass of the rubber component. Even more preferable. The upper limit of the amount is more preferably 50.0 parts by mass or less, even more preferably 40.0 parts by mass or less, and even more preferably 30.0 parts by mass or less. This amount can maintain workability in the manufacturing process.

Applications of the rubber composition of the present invention are not particularly limited, and examples include transportation equipment such as automobiles, trains, ships, and airplanes; electrical appliances such as personal computers, televisions, telephones, watches, etc.; mobile communication devices such as mobile phones. AV equipment such as portable music reproducing equipment and video reproducing equipment; printing equipment; copying equipment; sporting goods; building materials; Besides these, it can be applied to members using rubber or flexible plastic, and is suitable for application to tires. Examples of tires include pneumatic tires for passenger cars, trucks, buses, and heavy vehicles.

The rubber composition obtained by the present invention exhibits higher mechanical strength than rubber compositions containing no cellulose nanofibers. In addition, by using anion-modified cellulose nanofibers obtained by defibrating anion-modified cellulose using a cavitation jet device as the cellulose nanofibers mixed with the rubber component, power consumption can be reduced in the production process of the masterbatch and the rubber composition. can be reduced, and a rubber composition having high mechanical strength can be produced cost-effectively.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

<Production Example 1: Production of carboxylated cellulose nanofibers (cavitation fibrillation)>
5.00 g (bone dry) of bleached unbeaten kraft pulp (85% whiteness) derived from softwood, 39 mg (manufactured by Sigma Aldrich) of TEMPO (0.05 mmol relative to 1 g of bone dry cellulose) and 514 mg of sodium bromide ( 1.0 mmol per 1 g of absolute dry cellulose) was added to 500 mL of an aqueous solution and stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that sodium hypochlorite was 5.5 mmol/g, and an oxidation reaction was initiated at room temperature. The pH in the system decreased during the reaction, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the sodium hypochlorite was consumed and the pH in the system stopped changing. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain an oxidized pulp (carboxylated cellulose). At this time, the pulp yield was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.4 mmol/g. Water is added to the reaction mixture to adjust the concentration to 1% by mass (w/v), and cavitation treatment is repeatedly performed for 1 to 24 passes using a cavitation jet device at an upstream pressure of 9 MPa and a downstream pressure of 0.4 MPa. A cellulose nanofiber dispersion was obtained. The number of passes in cavitation treatment was calculated using the following formula:
Number of passes = Nozzle flow rate x Processing time / Amount of sample

<Production Example 2>
Oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Production Example 1, except that sodium hypochlorite was added to 6.0 mmol/g to initiate the oxidation reaction. At this time, the pulp yield was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol/g. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device (inside diameter of the pipe immediately after the nozzle was 2.3 cm) with an adjusted nozzle hole shape was used to set the upstream pressure to 9 MPa and the downstream pressure to 0. 24 passes of cavitation treatment were performed at 45 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 70%.

<Production Example 3>
Using 500 mL of an aqueous solution in which 80 mg of TEMPO (manufactured by Sigma Aldrich) (0.1 mmol relative to 1 g of absolute dry cellulose) and 800 mg of sodium bromide (1.47 mmol relative to 1 g of absolute dry cellulose) are dissolved, sodium hypochlorite An oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Production Example 1, except that the oxidation reaction was initiated by adding so that the concentration of cellulose was 8.6 mmol/g. At this time, the pulp yield was 86%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.9 mmol/g. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device equipped with the same nozzle as in Production Example 2 (the pipe inner diameter immediately after the nozzle was 2.3 cm) was used, and the upstream pressure was 9 MPa, and the downstream pressure was 9 MPa. 16 passes of cavitation treatment were performed at a pressure of 0.45 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 59%.

<Production Example 4>
Production example except that 20 mg of TEMPO (manufactured by Sigma Aldrich) (0.025 mmol with respect to 1 g of absolute dry cellulose) was used, and sodium hypochlorite was added so as to be 2.2 mmol / g to initiate the oxidation reaction. An oxidized pulp (carboxylated cellulose) was obtained in the same manner as in 1. At this time, the pulp yield was 93%, the time required for the oxidation reaction was 60 minutes, and the amount of carboxyl groups was 0.7 mmol/g. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device equipped with the same nozzle as in Production Example 2 (the pipe inner diameter immediately after the nozzle was 2.3 cm) was used, and the upstream pressure was 9 MPa, and the downstream pressure was 9 MPa. Cavitation treatment was performed 70 passes at a pressure of 0.40 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 61%.

<Production Example 5>
An oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Production Example 2. Water was added to the reaction mixture to adjust the concentration to 2.5% by mass, and a cavitation jet apparatus equipped with the same nozzle as in Production Example 2 (inside diameter of the pipe immediately after the nozzle was 2.3 cm) was used. Cavitation treatment was performed 63 times at a pressure of 0.40 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 62%.

<Production Example 6>
An oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Production Example 2. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device equipped with the same nozzle as in Production Example 2 (inside diameter of the pipe immediately after the nozzle was 2.9 cm) was used. Cavitation treatment was performed 30 passes at a pressure of 0.04 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 51%.

<Production Example 7>
An oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Production Example 2. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device equipped with the same nozzle as in Production Example 2 (inside diameter of the pipe immediately after the nozzle was 2.9 cm) was used. Cavitation treatment was performed 30 passes at a pressure of 0.27 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 50%.

<Production Example 8>
A carboxylated cellulose nanofiber dispersion was obtained in the same manner as in Production Example 6 except that the upstream pressure was 9 MPa, the downstream pressure was 0.45 MPa, and the inner diameter of the pipe immediately after the nozzle was 2.3 cm. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 65%.

<Production Example 9>
A carboxylated cellulose nanofiber dispersion was obtained in the same manner as in Production Example 8, except that the upstream pressure was 9 MPa and the downstream pressure was 0.63 MPa. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 66%.

<Production Example 10>
An oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Production Example 1. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device equipped with the same nozzle as in Production Example 2 (the pipe inner diameter immediately after the nozzle was 2.3 cm) was used, and the upstream pressure was 9 MPa, and the downstream pressure was 9 MPa. Cavitation treatment was performed 30 passes at a pressure of 0.54 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 60%.

<Production Example 11>
130 parts by mass of water and 20 parts by mass of sodium hydroxide dissolved in 100 parts by mass of water are added to a biaxial kneader whose rotation speed is adjusted to 100 rpm, and hardwood pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) is added. 100 parts by mass of the dry mass after drying at 100° C. for 60 minutes was charged. The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. Further, 230 parts by mass of isopropanol (IPA) and 60 parts by mass of sodium monochloroacetate were added with stirring, and after stirring for 30 minutes, the temperature was raised to 70° C. and carboxymethylation reaction was allowed to occur for 90 minutes. After completion of the reaction, the mixture was neutralized, deliquored, dried and pulverized to obtain a sodium salt of carboxymethylated cellulose having a degree of carboxymethyl substitution of 0.31 and a cellulose type I crystallinity of 67%. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device equipped with the same nozzle as in Production Example 2 (the pipe inner diameter immediately after the nozzle was 2.3 cm) was used, and the upstream pressure was 9 MPa, and the downstream pressure was 9 MPa. Cavitation treatment was performed 40 passes at a pressure of 0.40 MPa to obtain a carboxymethylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 63%.

<Production Example 12>
6.75 g of sodium dihydrogen phosphate dihydrate and 4.83 g of disodium hydrogen phosphate were dissolved in 19.62 g of water to obtain an aqueous solution of a phosphoric acid compound (hereinafter referred to as "phosphorylation reagent"). rice field. Water was added to unbleached softwood kraft pulp (NUKP, water content 80%, Canadian standard freeness (CSF) measured according to JIS P8121, 580 ml) so that the concentration was 4% by mass. After that, using a double disc refiner, the material was beaten to 200 ml of irregular CSF (plain weave 80 mesh, conforming to JIS P8121 except that the amount of pulp collected was 0.3 g) and the length average fiber length to 0.66 mm. The cellulose suspension thus obtained was diluted to 0.3%, and a pulp sheet (thickness: 200 µm) having a moisture content of 90% and a solid content (absolute dry mass) of 3 g was obtained by a papermaking method. This pulp sheet is immersed in 31.2 g of the phosphorylation reagent (80 parts by mass as the elemental amount of phosphorus with respect to 100 parts by mass of dry pulp), and after heating for 1 hour with a blower dryer (DKM400, Yamato Scientific Co., Ltd.) at 105 ° C. , and further heat-treated at 150°C for 1 hour to introduce phosphate groups into the cellulose fibers. Next, 500 ml of ion-exchanged water was added to the pulp sheet in which the phosphate group was introduced into the cellulose fiber, and after stirring and washing, dehydration was performed. The sheet after dehydration was diluted with 300 ml of deionized water, and 5 ml of 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a cellulose suspension having a pH of 12-13. Thereafter, this cellulose suspension was dehydrated and washed by adding 500 ml of deionized water. This dehydration wash was repeated two more times. The degree of phosphate group substitution at this time was 0.34. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device equipped with the same nozzle as in Production Example 2 (the pipe inner diameter immediately after the nozzle was 2.3 cm) was used, and the upstream pressure was 9 MPa, and the downstream pressure was 9 MPa. Cavitation treatment was performed 30 passes at a pressure of 0.4 MPa to obtain a phosphate-esterified cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the inner diameter of the pipe immediately after the nozzle was 61%.

<Production Example 13: Production of carboxylated cellulose nanofibers (high-pressure homogenizer fibrillation)>
Water was added to the reaction mixture (carboxylated cellulose) obtained in the same manner as in Production Example 1 to adjust the concentration to 1.0% by mass (w/v), and the mixture was homogenized with an ultrahigh pressure homogenizer (20°C, 150Mpa) from 1 to After three passes, a carboxylated cellulose nanofiber dispersion was obtained.

<Production Example 14: Production of carboxylated cellulose nanofibers (high-pressure homogenizer fibrillation)>
Water was added to the reaction mixture (carboxylated cellulose) obtained in the same manner as in Production Example 4 to adjust the concentration to 1.0% by mass (w/v), and the mixture was passed through an ultrahigh pressure homogenizer (20°C, 150 MPa) for 5 passes. processed to obtain a carboxylated cellulose nanofiber dispersion.

<Example 1>
A 1.0% by mass aqueous dispersion of the cellulose nanofibers of Production Example 1 above was mixed with natural rubber latex (trade name: HA Latex, Resitex, solid content concentration: 61.5% by mass). The mixing ratio of natural rubber latex (bone dry solids) and cellulose nanofibers (bone dry solids) was 5.0 parts by mass of cellulose nanofibers per 100 parts by mass of natural rubber latex. These were stirred with a TK homomixer (8000 rpm) for 30 minutes to obtain a mixture. The mixture was dried in a heating oven at 70°C for 15 hours.

The obtained mixture was mixed with 6.0% by mass of zinc oxide and 0.5% by mass of stearic acid relative to the rubber component in the mixture, respectively, and rolled at 30°C with an open roll (manufactured by Kansai Roll Co., Ltd.). A kneaded product was obtained by kneading for 10 minutes. To this kneaded product, sulfur and a vulcanization accelerator (BBS, Nt-butyl-2-benzothiazolesulfenamide) were added at 3.5% by mass and 0.7% by mass, respectively, based on the rubber component in the kneaded product. % and kneaded at 30° C. for 10 minutes using an open roll (manufactured by Kansai Roll Co., Ltd.) to obtain a sheet of an uncrosslinked rubber composition (masterbatch). The sheet of the uncrosslinked rubber composition thus obtained was sandwiched between molds and pressed at 150° C. for 15 minutes to obtain a crosslinked rubber sheet with a thickness of 2 mm.

The obtained crosslinked rubber sheet was cut into test pieces of a predetermined shape (dumbbell-shaped No. 3), and measured according to JIS K6251 "Vulcanized rubber and thermoplastic rubber - Determination of tensile properties" as a measure of tensile strength. , stress at 50% strain (M50), 100% strain (M100) and 300% strain (M300), and breaking strength were measured, respectively. A larger value indicates that the crosslinked rubber composition is better reinforced and has better mechanical strength.

<Examples 2 to 12>
Crosslinked rubber sheets of Examples 2 to 12 were obtained in the same manner as in Example 1, except that the cellulose nanofibers of Production Examples 2 to 12 were used instead of the cellulose nanofibers of Production Example 1.

<Comparative Example 1>
A crosslinked rubber sheet of Comparative Example 1 was obtained in the same manner as in Example 1, except that the cellulose nanofibers were not mixed.

<Reference Examples 1 and 2>
Crosslinked rubber sheets of Reference Examples 1 and 2 were obtained in the same manner as in Example 1, except that the cellulose nanofibers of Production Examples 13 and 14 were used.

Stress at 50% strain (M50), 100% strain (M100), and 300% strain (M300) of the crosslinked rubber sheets of Examples 1 to 12, Comparative Example 1, and Reference Examples 1 and 2, and rupture Table 1 shows the strength.

Further, in Production Examples 1 to 14, the amount of electric power consumed by the defibration device when defibrating anion-modified cellulose into anion-modified cellulose nanofibers, and the dispersion medium of water for the obtained anion-modified cellulose nanofibers. Table 1 shows the viscosity and the transparency of the dispersion (solid concentration: 1.0% by mass). The methods for measuring viscosity and transparency are as follows.

<Measurement of viscosity>
300 g of an aqueous dispersion is prepared in a glass beaker so that the solid content concentration of anion-modified cellulose nanofibers is 1.0% by mass. The water dispersion is heated to 25° C., and according to the method of JIS-Z-8803, a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) is used to measure the viscosity after 3 minutes at a rotation speed of 60 rpm or 6 rpm.

<Measurement of transparency>
After preparing an anion-modified cellulose nanofiber aqueous dispersion so that the solid content concentration is 1.0% by mass, a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) is used to obtain a square shape with an optical path length of 10 mm. Using a cell, the transmittance (%) of 660 nm light is measured and defined as transparency.

From the results in Table 1, it can be seen that the rubber compositions obtained in Examples 1 to 12 exhibit significantly higher mechanical strength than the rubber composition of Comparative Example 1 that does not contain anion-modified cellulose nanofibers.

In addition, in the methods of Examples 1 to 3 and 5 to 10 using a cavitation jet device during the production of carboxylated cellulose nanofibers, compared to the method of Reference Example 1 using an ultra-high pressure homogenizer, the amount of power consumption is less than that of the method using an ultrahigh pressure homogenizer. It can be seen that a rubber composition exhibiting mechanical strength can be produced. In addition, in the method using a cavitation jet device during the production of carboxylated cellulose nanofibers in Example 4, compared to the method using an ultra-high pressure homogenizer in Reference Example 2, the rubber composition exhibits mechanical strength equal to or greater than that with less power consumption. You know you can make things. In addition, the carboxymethylated cellulose nanofiber of Example 11 and the phosphate esterified cellulose nanofiber of Example 12 are also produced using a cavitation jet apparatus to produce cellulose nanofibers with low power consumption and high mechanical strength. know that it can be done.

In addition, it can be seen that the methods of Examples 1 to 3 and 5 to 10 can produce anion-modified cellulose nanofibers with high transparency and high viscosity with less power consumption than the method of Reference Example 1. . In addition, it can be seen that the method of Example 4 can produce anion-modified cellulose nanofibers having the same degree of transparency and high viscosity with less power consumption than the method of Reference Example 2. In addition, the carboxymethylated cellulose nanofiber of Example 11 and the phosphate-esterified cellulose nanofiber of Example 12 were also produced using a cavitation jet device, with low power consumption, high transparency, and high viscosity cellulose nanofibers. can be produced. The high transparency of the anion-modified cellulose nanofibers indicates that the defibration progressed uniformly. This indicates that there are few fibers with large . Higher viscosity also indicates less fiber damage. The ability to produce such highly transparent and highly viscous anion-modified cellulose nanofibers with low power consumption is advantageous in the production of masterbatches and rubber compositions because it leads to the production of products that are less likely to break at low cost. You can say that.

Claims (9)

Step 1 of preparing anion-modified cellulose,
Step 2 of defibrating anion-modified cellulose to produce anion-modified cellulose nanofibers using a cavitation jet device, and Step 3 of mixing the anion-modified cellulose nanofibers obtained in step 2 with a rubber component to obtain a masterbatch. ,
A method of manufacturing a masterbatch, comprising: When the anion-modified cellulose nanofibers produced in step 2 are anion-modified cellulose nanofiber dispersions with a solid content of 1.0% by mass using water as a dispersion medium, the wavelength is measured using a prismatic cell with an optical path length of 10 mm. 2. The method of claim 1, wherein the transmittance measured with 660 nm light is 37% or more. The cavitation jet device imparts an impact force to the anion-modified cellulose when the cavitation bubbles generated by the liquid jet jetted through the nozzle or orifice collapse, and the upstream pressure of the liquid jet jetted through the nozzle or orifice is 0.01 MPa. 3. The method according to claim 1 or 2 , wherein the pressure is not less than 30.00 MPa and the ratio of downstream pressure/upstream pressure is 0.001 to 0.500. The method according to any one of claims 1 to 3 , wherein the anion-modified cellulose is cellulose having carboxyl groups. 5. The method according to claim 4 , wherein the amount of carboxyl groups in the anion-modified cellulose is 0.4 mmol/g to 3.0 mmol/g relative to the absolute dry weight of the anion-modified cellulose. The method according to any one of claims 1 to 3 , wherein the anion-modified cellulose is cellulose having carboxymethyl groups. The method according to claim 6, wherein the anion-modified cellulose has a degree of carboxymethyl substitution of 0.01 or more and less than 0.40. The method of any one of claims 1-7 , wherein the rubber component comprises a diene-based rubber polymer. A method for producing a rubber composition, comprising a step of producing a masterbatch by the method according to any one of claims 1 to 8 , and a step of cross-linking the masterbatch.